1. Field of the Invention
The present invention relates to an indicator system for use in oil and gas operations. More particularly, the present invention pertains to an electro-mechanical indicator system for signaling when a droppable object (such as, for example, a dart, plug or ball) is released during well cementing operations.
2. Brief Description of the Prior Art
Conventional rotary drilling rigs typically comprise a supportive rig floor incorporating a rotary table, a substantially vertical derrick extending above said rig floor, and a traveling block or other hoisting mechanism that can be raised and lowered within said derrick. During drilling or servicing operations, such rig equipment is often used to manipulate tubular goods (such as drill pipe), through the rotary table and in and out of a well bore extending into the earth's crust. Once a well has been drilled to a desired depth, large diameter pipe called casing is frequently installed in such well and cemented in place. The casing is typically installed to provide structural integrity to a well bore, and to keep geologic formations isolated from one another.
When conventional drilling rigs are used, casing is typically inserted into a well in a number of separate sections of substantially equal length. Single sections of pipe called “joints,” are typically screwed together or otherwise joined end-to-end at the rig in order to form a substantially continuous “string” of pipe that reaches downward into the earth's surface. As the bottom or distal end of the pipe string penetrates further into a well, additional sections of pipe are added to the ever-lengthening pipe string at the rig.
Conventional casing operations typically involve specialized crews and equipment mobilized at a rig site for the sole purpose of running casing into a well. With conventional casing operations, powered casing tongs, casing elevators and spiders, and at least one dedicated hydraulic power unit are typically required to be mobilized to a well location and installed just prior to such casing operating. Specialized casing crews must rig up and operate the equipment, connect the joints of casing to run in the well, and demobilize the equipment following completion of the job.
Top drive systems, which can be used to pick up sections of pipe, connect pipe sections together, and provide the torque necessary to drill wells, have been used on drilling rigs for some time to make-up drill pipe connections and to efficiently drill wells. Until relatively recently, it has been a challenge to develop a viable method of using top drives systems to make-up and run casing strings, just as strings of drill pipe have historically been run. However, a method of running casing using a rig's top drive system together with a casing running tool (CRT) has become increasingly popular in recent years.
During casing running operations, especially those conducted using CRT's, specialized equipment known as cement heads are frequently utilized. Such cement heads should beneficially permit cement slurry to flow from a pumping assembly into a well, and should have sufficient flow capacity to permit high pressure pumping of large volumes of cement and other fluids at high flow rates. Such cement heads should also have sufficient tensile strength to support heavy weight tubulars extending from the surface into a well, and to accommodate raising and lowering of such tubular goods without interfering with and/or intermittently stopping longitudinal and/or rotational movement of a casing string.
Droppable objects, such as a dart, balls, plugs and/or other objects, which are typically constructed of rubber, plastic or other material, are frequently pumped into a well in connection with cementing operations. In many instances, such items are suspended within a cement head until the objects are released or “launched” at desired points during the cement pumping process. Once released, such items join the cement slurry flow and can be pumped down hole directly into a well. Such darts, balls, plugs and/or other objects should be beneficially held in place within the slurry flow passing through the cement head prior to being launched or released without being damaged or washed away by such slurry flow. Further, it is critically important to know when such droppable objects have been successfully launched and cleared the cement head, entering the wellbore below such cement head.
Indicator systems for detecting passage of such droppable objects, commonly known in the industry as “tattle tales,” have been developed for this purpose. Tattle tales are frequently used on cement heads to indicate that droppable objects such as a darts, plugs, balls or other objects have been released from a stationary position, passed through a cement head, and entered into the well below.
During well cementing operations, it is imperative that an operator must recognize that a droppable object is actually released, as well as the precise time when it is released. An absence of a positive indication of such release can be a serious problem. By way of example, but not limitation, failure to know when a plug is released can lead to miscalculation of a volume of cement needed to be pumped downhole through a cement head in order to adequately cement casing in place.
A challenge exists in finding a suitable sealing arrangement between the extremely harsh environment of the interior of a well, which can have fluids flowing at rates as high as eight barrels a minute with pressures of up to 15,000 PSI, and the atmospheric pressure encountered outside of the cement head. Moreover, wellbore fluids can be drilling mud or cement, which are typically non-homogeneous and difficult to seal against.
Prior art cementing heads typically utilize a mechanical lever-actuated indicator or tattle tale to indicate passage of a cementing plug from a plug holder within a cement head. In some instances, such prior art mechanical lever-actuated plug release indicators may erroneously signal the passage of a cementing plug from a cementing plug container within a cement head, even though such plug is still contained within the container. Such erroneous indications can ruin an otherwise effective cement job due to over displacement of cement.
Another type of prior art tattle tale utilizes a radioactive nail or other source incorporated into a cementing plug. When a cementing plug having a radioactive signature is no longer present in the cementing plug container (that is, after it is released), a radiation measuring instrument, such as a Geiger counter or the like, will indicate that the plug is no longer in the cementing plug container in the cement head. However, because the shelf life of readily available and easily handled radioactive nails is limited, such nails may be difficult to obtain and store, especially when working in remote areas.
Additionally, acoustic-type plug release indicators have also been used to indicate release of droppable objects. Such devices utilize at least one microphone to detect the sound of an object moving through well casing and transmit a signal to a listening system and, frequently, a magnetic tape recorder.
Yet another type of prior art tattle tale device uses a micro-switch or a reed magnetic switch. Both devices, unless carefully sealed, have the potential for causing a spark either when the switch closes or opens. Moreover, the switch contacts can become fouled and not allow a path for electrical current to flow when the switch is closed. Vibration in a drilling rig can also cause very sensitive contacts of such switches to make false contact or partial contact, thereby causing high resistance abnormalities in the circuit. Finally, this mechanical type of switch requires mechanical penetration and communication between a high pressure, hostile environment within a wellbore, and the environment outside the cement head where an indication must be observable.
Existing prior art indicator devices all suffer from significant operational and performance limitations. Thus, it is desirable to find a suitable means for transferring sensed data from the inner flow bore of a cement head through a suitable barrier or sealing means to an indicating device outside of said cement head. The indicator should reliably and consistently signal passage of a droppable object within said flow bore of a cement head.